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Allozyme variation in rock pool metapopulation of two species of waterfleas (Daphnia) is studied with the aim to understand how these dynamics influence genetic differentiation. The genetic population structure in metapopulation is explained by strong drift during colonization, local inbreeding, which results in hybrid vigor and increased effective migration rates after subsequent immigration and effects selection through hitchhiking of neutral genes with linked loci under selection.

Erlotinib is an orally active antitumor agent. Analyses in vitro using human liver microsomes and recombinant enzymes showed that erlotinib was metabolized primarily by CYP3A4, with a secondary contribution from CYP1A2. A computer-based simulation model, SimCYP™, predicted that CYP3A4 contributed to ∼70% of the metabolic elimination of erlotinib, with CYP1A2 being responsible for the other ∼30%. A drug-drug interaction study was therefore conducted for erlotinib and a potent CYP3A4 inhibitor, ketoconazole, in healthy male volunteers to evaluate the impact of CYP3A4 inhibition on erlotinib exposure. Ketoconazole caused an almost two-fold increase in erlotinib plasma area under the concentration curve and in maximum plasma concentration. This is consistent with the SimCYP™ prediction of a two-fold increase in erlotinib AUC, further validating a primary (∼70%) role of CYP3A4 in erlotinib elimination. Prediction of clinically important drug-drug interaction with SimCYP™ using in vitro human metabolism data can be a powerful tool during early clinical development to ensure safe administration of anticancer drugs, which are often co-administered at maximum tolerated doses with other drugs as part of a palliative treatment regimen. [ABSTRACT FROM AUTHOR]

Recently, serious infections related to the use of tofacitinib (TOF) for treatment of rheumatoid arthritis (RA) have raised considerable interest. This study aimed to compare the risk for serious infections in patients with RA upon receiving TOF versus biologic disease-modifying antirheumatic drugs (bDMARDs) by age at treatment initiation. We identified adult RA patients exposed to TOF or bDMARDs using data collected by the Swiss registry for inflammatory rheumatic diseases (SCQM) from 2015 to 2018. The event of interest was the first non-fatal serious infection (SI) during drug exposure. Missing or incomplete SI dates were imputed as either the lower (left) or upper (right) limit of the known occurrence interval. The ratio of SI hazards (HR) of TOF versus bDMARDs was estimated as a function of age using covariate-adjusted Cox regression applied to each type of imputed time-to-SI. A total of 1687 patients provided time at risk for a first SI during study participation and drug exposure for 2238 different treatment courses, 345 for TOF and 1893 for bDMARDs. We identified 44 (left imputation) or 43 (right imputation), respectively, first SIs (12/12 on TOF versus 32/31 on bDMARDs). Left and right imputation produced similar results. For patients aged ≥ 69 years, the treatment HR started to be increased (lower limit of 95% confidence intervals (LLCIs) > 1). By the age of 76, the difference between TOF and bDMARDs started to be clinically relevant (LLCIs > 1.25). For patients aged < 65 years, the data were insufficient to draw conclusions. Our results suggest that we should expect an increased risk for SIs in older patients treated with TOF compared to bDMARDs supporting a cautious use of TOF in these patients., (© 2023. Springer Nature Limited.)

Patients with inflammatory rheumatic diseases (IRD) are at increased risk for worse COVID-19 outcomes. Identifying whether mRNA vaccines differ in immunogenicity and examining the effects of immunomodulatory treatments may support COVID-19 vaccination strategies. We aimed to conduct a long-term, model-based comparison of the humoral immunogenicity following BNT162b2 and mRNA-1273 vaccination in a cohort of IRD patients. Patients from the Swiss IRD cohort (SCQM), who assented to mRNA COVID-19 vaccination were recruited between 3/2021-9/2021. Blood samples at baseline, 4, 12, and 24 weeks post second vaccine dose were tested for anti-SARS-CoV-2 spike IgG (anti-S1). We examined differences in antibody levels depending on the vaccine and treatment at baseline while adjusting for age, disease, and past SARS-CoV-2 infection. 565 IRD patients provided eligible samples. Among monotherapies, rituximab, abatacept, JAKi, and TNFi had the highest odds of reduced anti-S1 responses compared to no medication. Patients on specific combination therapies showed significantly lower antibody responses than those on monotherapy. Irrespective of the disease, treatment, and past SARS-CoV-2 infection, the odds of higher antibody levels at 4, 12, and 24 weeks post second vaccine dose were, respectively, 3.4, 3.8, and 3.8 times higher with mRNA-1273 versus BNT162b2 (p < 0.0001). With every year of age, the odds ratio of higher peak humoral immunogenicity following mRNA-1273 versus BNT162b2 increased by 5% (p < 0.001), indicating a particular benefit for elderly patients. Our results suggest that in IRD patients, two-dose vaccination with mRNA-1273 versus BNT162b2 results in higher anti-S1 levels, even more so in elderly patients., Competing Interests: KL reports personal fees from Gilead-Galapagos, Pfizer, Viatris, Celltrion, outside of the submitted work. AF has received research support from Abbvie, Eli-Lilly, Galapagos, and Pfizer outside of the submitted work, and consultancies or speaker honoraria for Abbvie, BMS, Eli-Lilly, Gilead, Pfizer, Sanofi, and UCB outside of the submitted work. AR-R reports honoraria for consultation and lectures from Abbvie, Amgen, Pfizer, Gilead, Novartis, Janssen, Eli-Lilly, Sanofi, Roche, UCB, BMS outside of the submitted work. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Raptis, Berger, Ciurea, Andrey, Polysopoulos, Lescuyer, Maletic, Riek, Scherer, von Loga, Safford, Lauper, Möller, Vuilleumier, Finckh and Rubbert-Roth.)

Objectives: To examine the effectiveness of tocilizumab (TCZ) with and without synthetic disease-modifying antirheumatic drugs (sDMARDs) in a large observational study., Methods: Patients with rheumatoid arthritis treated with TCZ who had a baseline visit and information on concomitant sDMARDs were included. According to baseline data, patients were considered as taking TCZ as monotherapy or combination with sDMARDs. Main study outcomes were the change of Clinical Disease Activity Index (CDAI) and TCZ retention. The prescription of TCZ as monotherapy was analysed using logistic regression. CDAI change was analysed with a mixed-effects model for longitudinal data. TCZ retention was analysed with a stratified extended Cox model., Results: Multiple-adjusted analysis suggests that prescription of TCZ as monotherapy varied according to age, corticosteroid use, country of the registry and year of treatment initiation. The change of disease activity assessed by CDAI as well as the likelihood to be in remission were not significantly different whether TCZ was used as monotherapy or in combination with sDMARDs in a covariate-adjusted analysis. Estimates for unadjusted median TCZ retention were 2.3 years (95% CI 1.8 to 2.7) for monotherapy and 3.7 years (lower 95% CI limit 3.1, upper limit not estimable) for combination therapies. In a covariate-adjusted analysis, TCZ retention was also reduced when used as monotherapy, with an increasing difference between mono and combination therapy over time after 1.5 years (p=0.002)., Conclusions: TCZ with or without concomitant sDMARDs resulted in comparable clinical response as assessed by CDAI change, but TCZ retention was shorter under monotherapy of TCZ., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Objectives: To investigate the impact of smoking on the response to treatment with a first tumour necrosis factor inhibitor (TNFi) in patients with axial spondyloarthritis (axSpA) in a real-life cohort., Methods: Patients fulfilling the Assessment of SpondyloArthritis international Society (ASAS) classification criteria for axSpA in the Swiss Clinical Quality Management Cohort were included in this study. The potential association between smoking status and differential response to TNFi in terms of the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Ankylosing Spondylitis Disease Activity Score (ASDAS) was analysed using multiple adjusted longitudinal mixed effect models. Binary response rates at 1 year were assessed with multiple adjusted logistic analyses., Results: A first TNFi was initiated in 698 patients with axSpA with available smoking status and a baseline or follow-up BASDAI assessment, of which 490 (70%) had complete covariate data. In comparison to non-smokers, current smokers demonstrated significantly smaller reductions in BASDAI and ASDAS scores upon treatment with TNFi (0.75 BASDAI units and 0.69 ASDAS units less, p=0.005 and 0.001, respectively) for patients with elevated baseline C-reactive protein (CRP) level. This effect was numerically smaller in patients with normal CRP. The odds for reaching a 50% improvement in BASDAI response or the ASAS criteria for 40% improvement after 1 year were significantly lower in current smokers than in non-smokers (0.54, 95% CI 0.31 to 0.95, p=0.03 and 0.43, 95% CI 0.24 to 0.76, p=0.004, respectively)., Conclusions: Current smoking is associated with an impaired response to TNFi in axSpA., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

Objectives: To determine the frequency of use of biologic DMARDs (bDMARDs) in monotherapy, to describe the baseline characteristics of patients treated with bDMARDs in monotherapy and to compare the effectiveness of bDMARDs in monotherapy with that of bDMARDs in combination with synthetic DMARDs (sDMARDs)., Methods: Using data from the Swiss RA (SCQM-RA) registry, bDMARD treatment courses (TCs) were classified either as monotherapy or as combination therapy, depending on the presence of concomitant sDMARDs. Prescription of bDMARD monotherapy was analysed using logistic regression. bDMARD retention was analysed using Kaplan-Meier and Cox models with the addition of time-varying covariate effects. Evolution of the DAS28 over time was analysed with mixed-effects models for longitudinal data., Results: A total of 4218 TCs on bDMARDs from 3111 patients were included, of which 1136 TCs (27%) were initiated as monotherapy. bDMARD monotherapy was preferentially prescribed to older, co-morbid patients with longer disease duration, lower BMI, more active disease and more previous bDMARDs. After adjusting for potential confounding factors, drug retention was significantly lower in monotherapy [hazard ratio 1.15 (95% CI: 1.03, 1.30)]. Other factors such as type of bDMARD and calendar year of prescription were associated with a stronger effect on drug retention. Response to treatment in terms of DAS28 evolution was also slightly but significantly less favourable in monotherapy (P = 0.04)., Conclusion: Our data suggest that bDMARD monotherapy is prescribed to more complex cases and is significantly less effective than bDMARD therapy in combination with sDMARDs, but to an extent that is clinically only marginally relevant., (© The Author 2015. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Documenting quality of life (QoL) in routine medical care and using it both for treatment and for clinical research is not common, although such information is absolutely valuable for physicians and patients alike. We therefore aimed at developing an efficient method to integrate quality of life information into the clinical information system (CIS) and thus make it available for clinical care and secondary use., Methods: We piloted our method in three different medical departments, using five different QoL questionnaires. In this setting we used structured interviews and onsite observations to perform workflow and form analyses. The forms and pertinent data reports were implemented using the integrated tools of the local CIS. A web-based application for mobile devices was developed based on XML schemata to facilitate data import into the CIS. Data exports of the CIS were analysed with statistical software to perform an analysis of data quality., Results: The quality of life questionnaires are now regularly documented by patients and physicians. The resulting data is available in the Electronic Health Record (EHR) and can be used for treatment purposes and communication as well as research functionalities. The completion of questionnaires by the patients themselves using a mobile device (iPad) and the import of the respective data into the CIS forms were successfully tested in a pilot installation. The quality of data is rendered high by the use of automatic score calculations as well as the automatic creation of forms for follow-up documentation. The QoL data was exported to research databases for use in scientific analysis., Conclusion: The CIS-based QoL is technically feasible, clinically accepted and provides an excellent quality of data for medical treatment and clinical research. Our approach with a commercial CIS and the web-based application is transferable to other sites.

Study Objective: To investigate the inhibitory potential of multiple doses of ritonavir-boosted saquinavir on the pharmacokinetics of oral midazolam, a cytochrome P450 (CYP) 3A4 model substrate., Design: Prospective, open-label, one-sequence, two-period crossover study., Setting: Clinical pharmacology unit in the United Kingdom., Participants: Eighteen healthy adult male and female volunteers (median age 37.5 yrs). Intervention. A single oral dose of midazolam 7.5 mg was administered on day 1. A second dose was administered on day 16, after 14 days of oral saquinavir 1000 mg-ritonavir 100 mg twice/day., Measurements and Main Results: Serial blood samples were taken for measurement of plasma concentrations of midazolam and its metabolite, 1'-hydroxymidazolam. Pharmacokinetic parameters of midazolam and 1'-hydroxymidazolam were determined when midazolam was given alone (day 1) and after coadministration with saquinavir-ritonavir for 14 days (day 16). Two weeks of treatment with saquinavir-ritonavir resulted in a 4.3-fold increase in maximum plasma concentration (C(max)) and a 12.4-fold increase in the area under the plasma concentration-time curve from time zero extrapolated to infinity (AUC(0-infinity)) for midazolam. Midazolam's half-life increased from 4.7 to 14.9 hours. Concomitant reductions for 1'-hydroxymidazolam were approximately 7-fold for C(max) and 2-fold for AUC(0-infinity). The 1'-hydroxymidazolam AUC(0-infinity):midazolam AUC(0-infinity) ratio was only 1% during coadministration of midazolam with saquinavir-ritonavir compared with 33% for midazolam alone. Adverse-event reports indicated that the combination of saquinavir, ritonavir, and midazolam was well tolerated but resulted in prolonged sedation., Conclusion: Administration of ritonavir-boosted saquinavir markedly increased the exposure of midazolam by inhibiting its metabolism, confirming that the combination of saquinavir and ritonavir at steady state strongly inhibits CYP3A4 activity.

This study was performed to determine the effect of two protease inhibitors, saquinavir (SQV, oral 1000 mg bid) boosted by ritonavir (RTV, oral 100 mg bid), on pharmacokinetics (PK) of methadone in opiate-dependent HIV-negative patients on stable methadone maintenance therapy. This was a two-center, open-label, one-sequence cross-over, multiple-dose study in 13 HIV-negative patients who were on stable methadone therapy (oral, 60-120 mg qd). All patients continued methadone treatment on days 2-15. All patients received SQV/RTV in combination with methadone from days 2-15. PK of methadone was assessed on day 1 (alone) and on day 15 when methadone treatment was combined with SQV/RTV at steady state. Twelve patients completed the study. Median age, body weight and height were 50 years (range: 24-54 years), 80 kg (range: 57-97 kg) and 174 cm (range: 163-189 cm), respectively. All patients were Caucasian, and 11 were smokers. Median methadone dose was 85 mg qd. Geometric mean area under curve of the plasma concentration-time curve over 24 hour dosing interval (AUC(0-24 hour)) ratio of methadone with and without SQV/RTV was 0.81% (90% confidence interval: 71-91%). There was no significant plasma protein-binding displacement of methadone by SQV/RTV. The combination of SQV/RTV and methadone was well tolerated. There were no clinically significant adverse events or significant changes in laboratory parameters, electrocardiograms or vital signs. The 19% decrease in R-methadone AUC(0-24 hour) in the presence of SQV/RTV was not clinically relevant. There appears to be no need for methadone dose adjustment when methadone (60-120 mg qd) and SQV/RTV (1000/100 mg bid) are coadministered.

OBJECTIVE: This study was designed to investigate the pharmacokinetic effects of coadministration of saquinavir/ritonavir with efavirenz at steady state. METHODS: Healthy volunteers in this open-label, two-arm, one-sequence, two-period crossover study (planned enrollment of 40 participants) were randomized to one of two treatment arms: those in Arm 1 were scheduled to receive saquinavir/ritonavir 1,000/100 mg orally twice daily for 29 days and efavirenz 600 mg orally once daily starting on day 15 and continuing through day 29; participants randomized to Arm 2 were to receive efavirenz once daily for 29 days and saquinavir/ritonavir 1,000/100 mg twice daily starting on day 15 through day 29. Assessments included vital signs, laboratory analyses, electrocardiography, and blood levels of total saquinavir, ritonavir, and efavirenz. Pharmacokinetic parameters included C(max) (maximum observed plasma concentration), t(max) (time to reach the maximum observed plasma concentration), (apparent elimination half-life), and AUC(0-tau) (area-under-the-plasma-concentration-time curve over one dosing interval). RESULTS: Eight participants (four in each arm) were enrolled; only two (one from each treatment arm) reached day 15 of the study and received the concurrent initial doses of saquinavir/ritonavir and efavirenz. The study was terminated prematurely after these two participants experienced nonserious adverse events. The participant in Arm 1 experienced mild abdominal discomfort, diarrhea, sleep disorder, and headache and the participant in Arm 2 experienced moderate-intensity abdominal pain and mild vomiting with leukocytosis accompanied by elevated pancreatic and hepatic enzymes (aspartate aminotransferase and alanine aminotransferase values of 2-fold and 3.5-fold the upper limit of normal, respectively). Both participants recovered completely following treatment discontinuation. Only limited pharmacokinetic data were generated on these two participants. CONCLUSIONS: The early termination of this study precluded drawing any definitive conclusions regarding the pharmacokinetics at steady state of coadministered saquinavir/ritonavir and efavirenz.

OBJECTIVES: Rifampin is a potent inducer of the cytochrome P450 3A4 isoenzyme (CYP3A4) that metabolizes most protease inhibitor (PI) antiretrovirals. This study was designed to evaluate the steady-state pharmacokinetics and tolerability of the coadministration of the PIs saquinavir and ritonavir (a CYP3A4 inhibitor used as a pharmacoenhancer of other PIs) and rifampin when coadministered in healthy HIV-negative volunteers. METHODS: In an open-label, randomized, one sequence, two-period crossover study involving 28 healthy HIV-negative volunteers, arm 1 was randomized to receive saquinavir/ritonavir 1000/100 mg twice daily while arm 2 received rifampin 600 mg once daily for 14 days. Both arms were then to receive concomitant saquinavir/ritonavir and rifampin for 2 additional weeks. Vital signs, electrocardiography, laboratory analyses, and blood levels of total saquinavir, ritonavir, rifampin, and desacetyl-rifampin, the primary metabolite of rifampin, were measured. RESULTS: In arm 1, 10/14 (71%) and, in arm 2, 11/14 (79%) participants completed the first study phase; eight participants in arm 1 and nine in arm 2 went on to receive both saquinavir/ritonavir and rifampin. Following substantial elevations (>/= grade 2) in hepatic transaminases in participants receiving the coadministered agents, the study was discontinued prematurely. Two participants in arm 1 displayed moderate elevations after five and four doses of rifampin, respectively. In arm 2, all participants experienced severe elevations within 4 days of initiating saquinavir/ritonavir. Clinical symptoms (e.g., nausea, vomiting, abdominal pain, and headache) were more common and severe in arm 2. Clinical symptoms abated and transaminases normalized following drug discontinuation. Limited pharmacokinetic data suggest a possible relationship between transaminase elevation and elevated rifampin and desacetyl-rifampin concentrations. CONCLUSIONS: Although not confirmed in HIV-infected patients, the data indicate that rifampin should not be coadministered with saquinavir/ritonavir.

The effects of food on the pharmacokinetics of erlotinib were investigated in two open-label, randomized studies. In a single-dose crossover study (n = 18), 150 mg of erlotinib was administered under either fasting or fed conditions. In the first period, an approximate doubling in the area under the plasma concentration-time curve was evidenced by the geometric mean ratio (GMR) of 2.09 observed under fed conditions; whereas, in the second period there was a decrease, with a GMR of 0.93. In a multiple-dose parallel study (n = 22), 100 mg of erlotinib was administered daily for 8 days, either 7 days of fasting followed by feeding on day 8, or the reverse sequence. In this study, food resulted in an increase in the plasma concentration-time curve on day 1, with a GMR of 1.66 (P = 0.015). In contrast, there was only a 37% increase on day 7, with a GMR of 1.34 (P = 0.252). These studies indicate that food can substantially increase plasma exposure to erlotinib. Given the maximum tolerated dose of erlotinib used in clinical practice, we recommend that erlotinib be taken under conditions of fasting.

The comorbidity of attention deficit hyperactivity disorder (ADHD) is frequently not well recognized in substance abuse treatment institutions in The Netherlands. As a consequence, patients with substance use disorder (SUD) and ADHD often receive suboptimal treatment. To prevent every treatment center from having to invent its own diagnostic procedure and intervention for ADHD, a national working group was established. This group developed an intervention program for the screening, diagnosis, and treatment of ADHD in patients with SUD. This article describes the development and content of this intervention program. An important part of this development was testing the intervention program in two addiction treatment centers in The Netherlands. Systematic screening of ADHD was part of the test. A self-report questionnaire was used. Subjects with positive screening results were referred for the diagnostic procedure. Nine hundred twenty-eight screenings were performed: 207 screened positive, 115 came for further diagnostics, and 65 were ultimately diagnosed with ADHD.

If colonization of empty habitat patches causes genetic bottlenecks, freshly founded, young populations should be genetically less diverse than older ones that may have experienced successive rounds of immigration. This can be studied in metapopulations with subpopulations of known age. We studied allozyme variation in metapopulations of two species of water fleas (Daphnia) in the skerry archipelago of southern Finland. These populations have been monitored since 1982. Screening 49 populations of D. longispina and 77 populations of D. magna, separated by distances of 1.5-2180 m, we found that local genetic diversity increased with population age whereas pairwise differentiation among pools decreased with population age. These patterns persisted even after controlling for several potentially confounding ecological variables, indicating that extinction and recolonization dynamics decrease local genetic diversity and increase genetic differentiation in these metapopulations by causing genetic bottlenecks during colonization. We suggest that the effect of these bottlenecks may be twofold, namely decreasing genetic diversity by random sampling and leading to population-wide inbreeding. Subsequent immigration then may not only introduce new genetic material, but also lead to the production of noninbred hybrids, selection for which may cause immigrant alleles to increase in frequency, thus leading to increased genetic diversity in older populations.

Objective: To establish the bioequivalence of a 500 mg film-coated tablet of saquinavir mesylate (FCT SQV) to the 200 mg hard-capsule saquinavir mesylate (HC SQV), both boosted with ritonavir and administered under fed conditions., Methods: We carried out a multi-centre, open-label, randomized, two-sequence, four-period, two-treatment, replicated crossover study in 93 healthy men and 7 healthy women. Individuals were randomly assigned to receive sequential single doses of saquinavir in one of two treatment sequences: ABAB or BABA. Individuals received 100 mg ritonavir twice daily for 24 days. On days 14,17, 20 and 23, study participants took 1000 mg of HC SQV (five 200 mg capsules, treatment A) or FCT SQV (two 500 mg tablets, treatment B) with a high-fat, high-calorie breakfast, and pharmacokinetic analyses were carried out over the next 24 hours. Area under the saquinavir concentration-time curve (AUC0-alpha), maximum saquinavir plasma concentration (Cmax), time to Cmax and terminal half-life were calculated. The relative bioavailability of FCT SOV versus HC SQV was calculated as the ratio of the respective estimated mean saquinavir AUC0-alpha and Cmax. The calculation was based on an ANOVA including the factors site, sex, sequence, period, treatment and study participant to the log-transformed parameters log(AUC0-alpha) and log(Cmax); the relative bioavailability and the 90% confidence intervals (CIs) were estimated using the treatment contrasts of the ANOVA. Bioequivalence was concluded as for both parameters, AUC0-alpha and Cmax, the 90% CIs for the relative bioavailability were entirely included in the reference region [0.80-1.25]., Results: Saquinavir plasma concentration-time profiles for the two formulations were similar. Geometric mean AUC0-alpha and Cmax values were clearly increased for FCT SQV (26 826 versus 24 430 h*ng/ml; and 3644 versus 3064 ng/ml, respectively); ratios of mean exposures were estimated to be 1.10 for AUC0-alpha and 1.19 for Cmax of saquinavir. However, the corresponding two-sided 90% CIs (1.04-1.16 and 1.14-1.25, respectively) all fell within the limits set for equivalence (0.80, 1.25). The adverse event profile for FCT SQV was similar to that for HC SQV., Conclusion: The new 500 mg FCT SQV formulation is bioequivalent to the 200 mg HC SQV formulation, at the dose of 1000 mg, in combination with 100 mg ritonavir under fed conditions. The 500 mg FCT SQV formulation reduces pill count for boosted saquinavir (SQV/r) from six capsules to three tablets twice daily. This may increase patient acceptability of SQV/r, particularly in less treatment-experienced patients.

The deleterious effects of inbreeding have long been known, and inbreeding can increase the risk of extinction for local populations in metapopulations. However, other consequences of inbreeding in metapopulations are still not well understood. Here we show the presence of strong inbreeding depression in a rockpool metapopulation of the planktonic freshwater crustacean Daphnia magna, which reproduces by cyclical parthenogenesis. We conducted three experiments in real and artificial rockpools to quantify components of inbreeding depression in the presence and the absence of competition between clonal lines of selfed and outcrossed genotypes. In replicated asexual populations, we recorded strong selection against clones produced by selfing in competition with clones produced by outcrossing. In contrast, inbreeding depression was much weaker in single-clone populations, that is, in the absence of competition between inbred and outbred clones. The finding of a competitive advantage of the outbred genotypes in this metapopulation suggests that if rockpool populations are inbred, hybrid offspring resulting from crosses between immigrants and local genotypes might have a strong selective advantage. This would increase the effective gene flow in the metapopulation. However, the finding of low inbreeding depression in the monoclonal populations suggests that inbred and outbred genotypes might have about equal chances of establishing new populations.

Immigrants to habitats occupied by conspecific organisms are usually expected to be competitively inferior, because residents may be locally adapted. If residents are inbred, however, mating between immigrants and residents results in offspring that may enjoy a fitness advantage from hybrid vigor. We demonstrate this effect experimentally in a natural Daphnia metapopulation in which genetic bottlenecks and local inbreeding are common. We estimate that in this metapopulation, hybrid vigor amplifies the rate of gene flow several times more than would be predicted from the nominal migration rate. This can affect the persistence of local populations and the entire metapopulation.

We have considered the extracellular serine protease thrombin and its receptor as endogenous mediators of neuronal protection against brain ischemia. Exposure of gerbils to prior mild ischemic insults, here two relatively short-lasting occlusions (2 min) of both common carotid arteries applied at 1-day intervals 2 days before a severe occlusion (6 min), caused a robust ischemic tolerance of hippocampal CA1 neurons. This resistance was impaired if the specific thrombin inhibitor hirudin was injected intracerebroventricularly before each short-lasting insult. Thus, efficient native neuroprotective mechanisms exist and endogenous thrombin seems to be involved therein. In vitro experiments using organotypic slice cultures of rat hippocampus revealed that thrombin can have protective but also deleterious effects on hippocampal CA1 neurons. Low concentrations of thrombin (50 pM, 0.01 unit/ml) or of a synthetic thrombin receptor agonist (10 microM) induced significant neuroprotection against experimental ischemia. In contrast, 50 nM (10 units/ml) thrombin decreased further the reduced neuronal survival that follows the deprivation of oxygen and glucose, and 500 nM even caused neuronal cell death by itself. Degenerative thrombin actions also might be relevant in vivo, because hirudin increased the number of surviving neurons when applied before a 6-min occlusion. Among the thrombin concentrations tested, 50 pM induced intracellular Ca(2+) spikes in fura-2-loaded CA1 neurons whereas higher concentrations caused a sustained Ca(2+) elevation. Thus, distinct Ca(2+) signals may define whether or not thrombin initiates protection. Taken together, in vivo and in vitro data suggest that thrombin can determine neuronal cell death or survival after brain ischemia.